Earthquakes A sudden and violent shaking of the ground as a result of movements within the earth's crust or volcanic action.

Focus – Point in the Earth where the plate moves Epicenter – Point on the Earth’s surface above the focus Fault – break in the crust where plates can move Aftershock – waves given off after an earthquake Foreshock – waves given off before an earthquake

FAULT: a break or crack along which rocks move - Rocks on one side of the fault slide past the rocks on the other side of the fault - Movements can be up, down, or sideways EARTHQUAKES Two blocks of rock form at a fault - one on top of the other Hanging wall: the block of rock above the fault Footwall: the block below the fault Stress can cause either the hanging wall or the footwall to move up or down along a fault

TYPES OF PLATE STRESSES FILL OUT THE CHART ON PAGE 14 WITH THE FOLLOWING INFORMATION SAN ANDREAS FAULT, CA. TYPES OF PLATE STRESSES Hanging wall moved UP relative to the foot wall REVERSE Hanging wall moved DOWN relative to the foot wall NORMAL Hanging wall moved up and OVER the foot wall REVERSE THRUST 2 plates move horizontally not vertically LATERAL

Label the picture on page 15 in your notes with: Focus Epicenter Fault Footwall Hanging wall

Elastic Rebound Hypothesis Pressure builds up until the stress is too great and the plates move quickly, releasing energy  This is the earthquake! To imagine this, press your hand down on your desk hard and try to move it forward. Pressure builds up until all of a sudden your hand jerks forward. This is similar to what’s happening with the plates – Pressure builds up and then the plates quickly release.

Measuring Earthquakes

Measuring Earthquakes Seismograph – instrument that records an earthquake’s waves Seismogram – Paper that records the earthquake waves in the seismograph machine

Body Waves Body waves, or Primary (P) waves and Secondary (S) waves, travel along Earth’s interior

P-WAVES - Push (compress) and pull (expand) in the direction that the waves travel - Have the greatest velocity of all earthquake waves - Travel through solids, liquids, and gases

S-WAVE Shake particles at right angles to the direction that they travel (up and down movement) - Travel only through solids - Slower velocity than P-waves

L-WAVES Travel at Earth’s surface (can only move through solids) Love Wave Rayleigh Wave L-WAVES (Surface waves) Travel at Earth’s surface (can only move through solids) R Waves - Move up and down like a water wave L Waves – Move side to side Slowest waves Surface waves cause the most damage.

Table 1. Main types of seismic waves. P waves (or "longitudinal waves") travel through fluids, and solids. S waves depends on the shear strength of the material. Surface waves are very similar to ocean waves as they only occur at the surface of the earth and do not penetrate into the interior deeply.   There are two types of surface waves: Love waves (L-Wave) and Rayleigh waves (R-Wave). Table 1.  Main types of seismic waves. wave type particle motion name body waves longitudinal P wave transverse S wave surface waves horizontal transverse Love wave vertical elliptical Rayleigh wave

Movement of the 3 Types of Waves

Movement of the 3 Types of Waves The difference in wave speed between P and S waves affects when each wave arrives at a location. This difference in arrival time allows us to determine distance from the epicenter! Now answer the question on page 15: “Which city is located farthest from the epicenter?”

TRIANGULATION: the process of determining the location of a source from known points -In order to find the exact location of an earthquake, there must be at least 3 seismic stations

Intensity – a measure of the amount of shaking at a given location (based on the amount of damage) Magnitude – a measure of the size of seismic waves (or the amount of energy released)   

Measuring Earthquakes 1. Richter Scale (Outdated scale) • Does not estimate adequately the size of very large earthquakes Based on the amplitude of the largest seismic wave 2. Moment Magnitude • Estimates energy released by an earthquake Derived from the amount of displacement that occurs along the fault zone • Measures very large earthquakes 3. Mercalli Scale Measures the intensity of shaking

LIQUIFACTION Tilted Victorian home at Howard and 17th Streets in the Mission District of San Francisco showing liquefaction-related damage from the 1906 earthquake. This area is underlain by marsh deposits that were covered by artificial fill in the middle to late 1800s. The earthquake shaking caused the artificial fill to liquefy and lose its ability to support the house. (Photograph U.S. Geological Survey)

LANDSLIDES With many earthquakes, the greatest damage to structures is from landslides and ground subsidence, or the sinking of the ground triggered by vibrations.

FIRE In the San Francisco earthquake of 1906, most of the destruction was caused by fires that started when gas and electrical lines were cut.

TSUNAMIS A tsunami triggered by an earthquake occurs where a slab of the ocean floor is displaced vertically along a fault.

Why is it important to study earthquakes? They affect our lives To better prepare for future earthquakes (improve building technologies) To gather information/data on where they occur, how often, how intense. Allow us to obtain information about the Earth’s interior

Answer questions 1-4 on page 14 of your packet Use the image to the right to answer Question 4 

LOOK AT PAGE 14 IN YOUR PACKET AND USE THE GRAPH TO ANSWER THE QUESTIONS FOR THE QUICK LAB!  THIS IS THE GRAPH THAT IS USED TO TRIANGULATE LOCATIONS OF EPICENTERS!